The present invention relates to a new and improved cardan-type pipe joint with compensation for longitudinal expansion.
Generally speaking, the cardan-type pipe joint of the present development is of the type possessing flanges for the attachment of main pipe sections which are to be connected, and at least one corrugated pipe interposed between the above-mentioned flanges. This corrugated pipe permits the flanges to shift with respect to each other in the longitudinal direction. There is also provided a cardan joint with two pairs of bolts, which enables the flanges to execute angular movements relative to each other.
In steam turbine plants where the steam under-goes interstage superheating before it enters the low-pressure section of the plant, the connecting line between the interstage superheater and the low-pressure turbine or turbines, conventionally comprises two or three pipe sections, the joint-members between these sections being designed in such a manner that the latter can yield, as far as possible without resistance, to the changes in length and angle which are caused by the thermal expansions. It is conventional practice to use three joint-elements which can move according to the cardan principle, two or these elements being attached, respectively, to the casing or shell of the interstage superheater and the casing of the low-pressure turbine, while the third and central element connects the pipe sections which are attached to the first two joint-elements. This type of design requires no length compensation, since the changes in length are taken up by the central joint-element, which can shift freely.
Another conventional design requires only two connection or joint-elements, one of which is seated on the turbine casing, and the other on the casing or shell of the interstage super-heater, and which are connected by a single pipe. Since, in this design, the two joint-elements are spatially fixed, one of them must allow the pipe, which is located between them, to expand or contract in the axial direction, as its temperature varies. The joint-element provided for this purpose, a so-called "universal compensator", is a component or structure involving considerable expense and which, as a result of its design, requires a large amount of space in the axial direction of the connecting line between the turbine and the interstage superheater.
This last-mentioned disadvantage is shared by the connecting line employing "universal compensators" and the first-mentioned design employing three cardan-type joint elements. The large amount of space required by the connecting line, which is always arranged horizontally, determines the distance between the turbine and the interstage superheater, and thereby also determines the site-area requirement for the plant and the dimensions of the machinery hall.
A further disadvantage of the "universal compensator" resides in the fact that its resistance to movement, especially to transverse movements, is relatively high, this being due to its structure, incorporating a system of rods, which connects the ends of the pipes. This resistance can cause harmful distortions to occur during operation, leading to overstressing of the material.